1. Field of the Invention
The present invention relates to data processing systems, and more particularly, to a data processing system with data transmission failure recovery measures wherein a system down is prevented in order to allow continuation of data transmission when there is failure during data transmission.
2. Description of the Background Art
FIG. 7 shows a conventional POS (Point of Sales) system with data transmission failure recovery measures. Referring to FIG. 7, a POS system 50 includes a plurality of POS terminals 51, a file server 52, a backup file server 53, and a host computer 55. Each POS terminal 51 is used for registering sales data into the system. File server 52 stores commodity name data, price data for each commodity code (price look up code: PLU code) corresponding to a bar code, as well as data indicating the amount of purchased commodities (commodity proceeds) data and numbers of purchased commodities (purchased commodity quantity) data in a file. Backup file server 53 is used as a backup in case of failure in file server 52. File server 52 and backup file server 53 are connected via a transmission line 54 for transmitting data between each other, so that the stored contents in file server 52 is always identical to that in backup file server 53. Host computer 55 accumulates and monitors sales data provided from each of POS terminals 51. POS terminals 51, file server 52, backup file server 53 and host computer 55 are connected to each other via transmission lines 56 and 57.
Transmission line 56 is used for normal transmission, whereas transmission line 57 is used when there is failure in transmission line 56.
In the case of registering sales data into the system, POS terminal 51 accesses file server 52 via transmission line 56 under normal transmission. Data such as price data corresponding to the PLU code requested from POS terminal 51 is read out from file server 52 to be provided to that POS terminal 51 via transmission line 56. File server 52 has commodity proceeds data and purchased commodity quantity data corresponding to the requested PLU code updated. The updated data are provided to backup file server 53 via transmission line 54, whereby the stored contents in backup file server 53 is updated according to the updated data, so that the stored contents of both file servers are always identical to each other after completion of the update.
In cases where failure occurs in transmission line 56 such that transmission cannot be carried out, each of POS terminals 51, file server 52, and host computer 55 automatically switch from transmission line 56 to transmission line 57 to continue transmission.
In cases where failure occurs in file server 52, each of POS terminals 51 and host computer 55 automatically access backup file server 53. The POS system of FIG. 7 includes dual transmission lines and file servers so that data transmission can be continued even if there is failure in the transmission lines or the file servers, avoiding a system down.
Although the above described conventional POS system has dual transmission lines and file servers for avoiding system down due to transmission failure, only one of the two transmission lines and the two file servers are used during normal transmission. The other transmission line and file server are not used as long as failure does not occur during data transmission.
Because the number of POS terminals installed in a POS system has recently been increasing, access to a file server is likely to be frequent and concentrated. This causes the a problem that the data processing speed of the POS terminals and the POS system is reduced. As a result it is desirable to use the backup file server at the time of normal transmission.